This invention relates to a ground coil used in a so-called ground primary-type magentically levitated railway in which a vehicle is equipped with superconducting coils.
In a so-called ground primary-type magentically levitated railway in which a vehicle is equipped with superconducting coils, use is being made of a side-wall levitation-guidance system in which the left and right side walls of a guideway are equipped with conductor coils for levitation, and corresponding locations of the left and right ground coils are connected by null-flux wiring. Also being used is a side-wall propulsion-levitation-guidance system in which wiring for propulsion is connected to terminals for the null-flux wiring.
Such a side-wall levitation-guidance system and the side-wall propulsion-levitation-guidance system have already been proposed as U.S. Pat. No. 4,913,059 by the inventors of the present invention.
Ground coils of the side-wall levitation-guidance type according to the prior art will now be described with FIGS. 1 through 4.
Conductor coils 14, 14' for propulsion are arranged in opposed relation on both inner side walls of a U-shaped track bed 9 at predetermined intervals along the direction in which the vehicle travels. As shown in FIG. 2, a three-phase propulsion power supply 20 (a polyphase motor of more than three phases can be employed if desired) is connected to the conductor coils 14, 14' for propulsion. Though the propulsion conductor coil 14' disposed on the nearer side wall of the track bed is deleted from FIG. 2, the propulsion conductor coil 14' is disposed on the nearer side wall of the track bed in the same manner as the propulsion conductor coil 14, and a propulsion power supply 20' is connected to it in the same fashion. Conductor coils 15, 15' for levitation and guidance are disposed in opposed relation on the sides of the propulsion conductor coils 14, 14' facing the superconducting coils 1, 1' and are arranged at predetermined intervals continuously along the direction in which the vehicle travels. Each conductor coil 15 comprises a null-flux connected upper coil 16 and lower coil 17 of the same shape and dimensions, and each conductor coil 15' comprises a null-flux connected upper coil 16' and lower coil 17' of the same shape and dimensions. These opposing conductor coils 15, 15' for levitation and guidance in turn are null-flux connected via connecting wires 18, 19.
The design is such that when the vehicle VH has its auxiliary wheels 7, 7' in contact with the track bed, the vertical midpoints of the superconducting coils 1, 1', the vertical midpoints of the levitation and guidance conductor coils 15, 15' and the vertical midpoints of the propulsion conductor coils 14, 14' lie on the same horizontal line. The upper coils 16, 16' and lower coils 17, 17' of the levitation and guidance conductor coils 15, 15' are vertically symmetrically positioned about respective predetermined points on the horizontal line. Further, numeral 4 denotes the truck of the vehicle VH, and numerals 5, 5' designate mechanical guiding wheels rotatably supported on one end of respective shafts 6, 6' the other ends of which are secured to the vehicle VH.
The arrangement described above is such that in response to introduction of power from the propulsion power supply 20, currents having the same direction as shown in FIG. 2 flow into the propulsion conductor coil 14 so that a propulsive force is produced by each of the vertical segments.
When the vehicle VH is running with its auxiliary wheels 7, 7' in contact with the track bed, the linkage flux developed by the conductor coils 15, 15' for levitation and guidance is zero, the current is zero and the electromagnetic resistance is zero. The reason for this is that the positional relationship between the superconducting coils 1, 1' and conductor coils 15, 15' for levitation and guidance is designed as set forth above, while the upper coil 16 and lower coil 17 are null-flux connected, as well as the upper coil 16' and lower coil 17'.
When the vehicle VH is running while levitated with its wheels 7, 7' raised, the vertical midpoints of the superconducting coils 1, 1' drop below the vertical midpoints of the conductor coils 15, 15' for levitation and guidance, as a result of which a difference is produced in the linkage magnetic flux between the upper coil 16' and lower coil 17'. At such time, currents as shown in FIG. 3 are induced in the upper coil 16 and lower coil 17 and in the upper coil 16' and lower coil 17'. In consequence, an attractive force acts between horizontal segments 16a, 16'a of the two upper coils 16, 16' and the upper horizontal segments of the superconducting coils 1, 1', while a repulsive force acts between horizontal segments 17a, 17'a of the two lower coils 17, 17' and the lower horizontal segments of the superconducting coils 1, 1'. Owing to these repulsive and attractive forces, a levitating force is produced that attempts to return the superconducting coils 1, 1' in the upward direction, with the coils 1, 1' attaining stability at a position where the weight of the vehicle vH is counterbalanced. Since the upper coil 16 and lower coil 17 as well as the upper coil 16' and lower coil 17' generate the levitating force effectively with little current, there is little electromagnetic traveling resistance.
The superconducting coils 1, 1' are arranged symmetrically with respect to the longitudinal center line of the track bed 9, and the opposing upper coils 16, 16' and opposing lower coils 17, 17' are null-flux connected via the connecting wires 18, 19. Therefore, when the vehicle VH is situated in the middle of the track bed, the linkage flux does not become zero even though there is no lateral displacement of the vehicle VH in the levitated state. However, since the linkage fluxes of the conductor coils 15, 15' for levitation and guidance are equal, currents do not flow through the connecting wires 18, 19. As a result, no lateral force is produced.
If the vehicle VH shown in FIG. 1 is displaced leftward, for example, during levitated travel, a difference develops in the linkage flux between the upper coils 16, 16' and between the lower coils 17, 17'. When the superconducting coils 1, 1' cope with this change in the linkage flux, currents as shown in FIG. 4 are induced in the levitation and guidance coils 15, 15', whereby a guidance force is produced that restores the superconducting coils 1, 1' to the middle of the track. In other words, repulsive forces act between the horizontal segment 16a of the upper coil 16 and the upper horizontal segment of superconducting coil 1, and between the horizontal segment 17a of the lower coil 17 and the lower horizontal segment of superconducting coil 1, while attractive forces act between the horizontal segment 16a' of upper coil 16' and the upper horizontal segment of superconducting coil 1', and between the horizontal segment 17'a of lower coil 17a and the lower horizontal segment of superconducting coil 1'. These forces restore the superconducting coils 1, 1' to the middle of the track.
Next, a conventional ground coil of the side-wall propulsion-levitation-guidance type will now be described with reference to FIGS. 5, 6(a), 6(b) and 6(c).
In comparison with the ground coil of the side-wall levitation-guidance type described above, this example differs mainly in that conductor coils corresponding to the propulsion conductor coils 14, 14' in the aforementioned side-wall levitation-guidance system are not provided, and in that conductor coils having the same construction as the levitation and guidance conductor coils 15, 15' of the levitation-guidance-conductor coils 15, 15' in the aforementioned side-wall levitation-guidance system are made to perform the functions of levitation, propulsion and guidance.
As shown in FIG. 5, conductor coils 21, 21' are disposed in opposed relation on both inner side walls of the U-shaped track bed 9 and are arranged at predetermined intervals continuously along the direction in which the vehicle travels. This structure is similar to that of the levitation and guidance conductor coils 15, 15' in the side-wall levitation-guidance system. That is, the conductor coil 21 (21') comprising a null-flux connected upper coil 22 (22') and lower coil 23 (23') having the same shape and dimensions, and the opposing conductor coils 21, 21' on both inner side walls of the U-shaped track bed 9 are null-flux connected. When the vehicle VH is in contact with the ground via its auxiliary wheels 7, 7', the vertical midpoint of the conductor coil 21 and the vertical midpoint of the superconducting coil 1 lie on the same horizontal line, and the upper coil 22 and lower coil 23 are disposed symmetrically about a predetermined point on this horizontal line. The conductor coil 21' also has exactly the same structure and arrangement as the conductor coil 21. In addition, the upper coil 22' corresponds to the upper coil 22, and the lower coil 23' corresponds to the lower coil 23.
A three-phase power supply (or a polyphase power supply of more than three phases) 26 for propulsion is connected to connecting wires 24, 25 which null-flux connect the opposing conductor coils 21, 21'. In a case where a three-phase power supply is used as the propulsion power supply, the arrangement is such that the phases are connected successively to every third conductor coil.
By introducing power from the propulsion power supply 26 to the above-described arrangement, a current for propulsion flows through the conductor coil 21 via a node 27 of connecting line 24 from a to a node 27' through b, c and d, and from e to the node 27' through f, g and h, and a current for propulsion flows through the conductor coil 21' via the node 27' from a' to the node 27' through b', c' and d' and from e' to the node 27' through f', g' and h', as shown in FIG. 6(a). Currents having the same direction, which is indicated by the arrows, flow through each of the coils 22, 23, 22', 23'. A propulsion force is produced by the generation of an electromagnetic flux in the forward direction of the vehicle VH between the vertical segments of the conductor coils 21, 21', namely the segments a-b, c-d, e-f, g-h, a'-b', c'-d', e'-f', g'-h', and the vertical segments of the superconducting coils 1,1'.
Meanwhile, forces for levitation and guidance are generated in the same manner as described above in conjunction with FIGS. 3 and 4. This will be explained again with reference to FIGS. 6(b) and 6(c).
When the vehicle VH is running on its wheels 7, 7', the linkage flux developed by the conductor coils 21, 21' for levitation and guidance is zero, the current is zero and the electromagnetic resistance is zero. The reason for this is that the positional relationship between the superconducting coils 1, 1' and conductor coils 21, 21' is designed as set forth above, while the upper coil 22 and lower coil 23 are null-flux connected, as well as the upper coil 22' and lower coil 23'. When the vehicle VH is running while levitated, the vertical midpoints of the superconducting coils 1, 1' drop below the vertical midpoints of the conductor coils 21, 21', as a result of which a difference is produced in the linkage magnetic flux between upper coil 22 and lower coil 23 and between upper coil 22' and lower coil 23'. Currents as shown in FIG. 6(b) are induced in the upper coils 22, 22' and lower coils 23, 23'. Owing to repulsive and attractive forces between horizontal segments of the coils 22, 23, 22', 23', a levitating force is produced that attempts to return the superconducting coils 1, 1' in the upward direction, with the coils 1, 1' attaining stability at a position where the weight of the vehicle VH is counterbalanced, in a manner the same as that set forth above.
The superconducting coils 1, 1' are arranged symmetrically with respect to the longitudinal center line of the track bed 9, and the opposing upper coils 22, 22' and opposing lower coils 23, 23' are null-flux connected via the connecting wires 24, 25. Therefore, when the vehicle VH is situated in the middle of the track bed 9, the linkage flux does not become zero even though there is no lateral displacement of the vehicle VH in the levitated state. However, since the linkage fluxes of the conductor coils 21, 21' are equal, currents do not flow through the connecting wires 24, 25. As a result, no lateral force is produced.
If the vehicle VH shown in FIG. 5 is displaced leftward, for example, during levitated travel, a difference develops in the linkage flux between the superconducting coils 1, 1' and the upper coils 22, 22' and between the superconducting coils 1, 1' and the lower coils 23, 23'. As a result, currents as shown in FIG. 6(c) are induced, whereby a guidance force is produced that the restores the superconducting coils 1, 1' to the middle of the track in the manner described above.
In the examples described above, a track bed having a U-shaped cross section is used as the track bed 9. However, it is possible to employ a track bed having a projecting-type cross section.
Specifically, as shown in FIG. 7, superconducting coils 31, 31' are vertically mounted on both inner side surfaces of a generally box-shaped truck 30 of the vehicle VH, and conductor coils 32, 32' for performing levitation, propulsion and guidance functions, as described above in conjunction with the side-wall propulsion-levitation-guidance system, are arranged on both side walls of a projecting track bed 38 so as to be capable of electromagnetically coupling with the superconducting coils 31, 31'. The conductor coil 32 has upper and lower coils 33, 34, respectively, and the conductor coil 32' has upper and lower coils 33', 34', respectively. The conductor coils 32, 32' are connected by connecting wires 39, 40. Auxiliary wheels 37, 37' are raised when the vehicle VH is running while levitated. When vehicle speed drops below a certain level, the auxiliary wheels 37, 37' are extended from the vehicle VH and make contact with the track bed 38. Mechanical guidance wheels 35, 35' are rotatably mounted on the ends of respective shafts 36, 36' whose other ends are fixedly secured to the vehicle VH. These wheels 35, 35' are deployed and guide the vehicle VH mechanically while rolling along the side walls of the projecting track bed 38 when the vehicle VH is running on its wheels 37, 37'.
When a vehicle of extended length that allows an increase in passenger capacity is introduced in order to increase the transportation capacity of the magnetically levitated railway, it is necessary to take into consideration the fact that the levitating force of the magnetically levitated vehicle should be increased in comparison with that of a shorter vehicle having a smaller passenger capacity. It is also necessary to take into account the fact that when the magnetically levitated vehicle is traveling on a curved section of the railway, the guiding force should be increased in comparison with that needed when the vehicle is traveling on a straight section of the railway. Still another consideration is that when the vehicle is traveling on an upgrade section of the railway or on a section located in a tunnel, the propulsive force should be increased in comparison with that needed when the vehicle is traveling on a flat section of the railway or on sections located outside tunnels.
However, in the case of a ground coil in the conventional side-wall levitation-guidance system or side-wall propulsion-levitation-guidance system described above, the characteristics thereof are decided by the fact that the design factors of levitating force and guiding force are mutually restrictive in the side-wall levitation-guidance system and the design factors of propulsive force, levitating force and guiding force are mutually restrictive in the side-wall propulsion-levitation-guidance system owing to such design requirements as the number of windings of the conductor coils, the shape of the coils and the characteristics of the coils. In other words, the problem is that levitating force and guiding force in the former system, and propulsive force, levitating force and guiding force in the latter system, cannot be designed independently of each other.
Accordingly, when the levitating force is raised in the side-wall levitation-guidance system, the guiding force also is strengthened. When the levitating force is raised in the side-wall propulsion-levitation-guidance system, the propulsive force and guiding force also rise since these forces are linked to the guiding force.
In a case where the levitating force is raised, it is necessary to increase the ampere turns of the side-wall conductor coils for levitation. When the ampere turns of the side-wall conductor coils for levitation are increased, the voltage of the null-flux wiring for obtaining the guiding force rises. This increased voltage cannot be accommodated by low-voltage electric wires.
An object of the present invention is to provide ground coils for a magnetically levitated railway capable of smooth operation conforming to railway traveling conditions and vehicle conditions in which it is possible to obtain a levitating force suited to an increase in the weight of the vehicle body of a vehicle of extended length, a guiding force suited to curved sections of the railway and a propulsive force suited to tunnel sections and upgrade sections of the railway, this being achieved by designing propulsive force, levitating force and guiding force independently of one another.